While lead acid batteries aren't the greatest, they are cheaper than other choices and provide a solution to those of us who can't afford better.
I'm not convinced they're all that much cheaper, especially when supporting larger loads like a microwave or toaster oven. e.g.. T105 has a nominal 250Ah rating but rating falls to just 166Ah with a 100A (~1000W AC) load like a toaster oven or microwave. Assuming we only want to discharge to 50% for maximum life that gives us 83Ah of usable energy.
I'm not sure what prices are like over that side of the pacific but here 2 x T105s will set you back $615 (
http://www.rpc.com.au/catalog/trojan-t105-p-46.html)
A 100Ah lithium battery is just a few clams more @ $674 (
http://ev-power.com.au/webstore/ind...es-1/12v-4-cell-100ah-lfp-battery-module.html)
The sticker might say 250Ah vs 100Ah but in the case of larger loads the lithium will provide similar usable energy (80Ah) for a significantly higher number of cycles - somewhere between 2000 and 4000 depending on who you ask (although i don't know anyone who's done anywhere near these figures yet)
Lead needs long absorption charging times to get from 80% SoC to 100% too, which doesn't really suit charging from solar whereas lithium will accept any charge rate over the whole SoC range so your batteries will be fully charged much quicker with Lithium.
Then there is weight... T105s = 56Kg , Lithium = 12.5Kg
Horses for courses but I think lithium is getting close to price parity for some systems based on how they're used and charged. Don't judge a book by its cover, or a battery by its Ah sticker